1. Field of the Invention
The present invention relates to a method of correcting light proximity effect, and more particularly relates to a method for efficiently correcting light proximity effect for data on photomask pattern.
2. Description of the Background Art
Miniaturization of a semiconductor device has been accompanied by such problems as deterioration in precision of finished dimension as well as change in a shape of an interconnection pattern due to the light proximity effect produced in a semiconductor element constituting the semiconductor device.
Depending on arrangement (such as line width, pitch) of a pattern formed on a photomask, optical image of exposure light transmitted through the photomask varies. This causes an error in the finished dimension of a resist film. This phenomenon is referred to as the light proximity effect. For example, assume that a resist film is exposed using a shading pattern of a photomask having patterns P100 and P200, and an interconnection layer is patterned using the patterned resist film as shown in FIG. 13A. Shapes of interconnection patterns P100a and P200a change considerably, especially at the middle portions where the interconnection patterns oppose to each other as shown in FIG. 13B.
Main problems developed presently include shortening of a gate pattern of a logical semiconductor device, and error of a pattern width when the pattern width is constant but pitch is changed. Therefore, correction of light proximity effect has been studied recently.
According to a method of correcting light proximity effect now employed, as shown by the flow chart of FIG. 14, photomask data is prepared in step 100 (hereinafter referred to as S100), a light distribution simulation and a development simulation are carried out based on the photomask data in S200. Following the result of the simulations, a correction value for light proximity effect is determined in S300.
In S400, the photomask data is corrected based on the correction value for light proximity effect obtained in S300. Next in S500, using the corrected photomask data, the light distribution simulation and development simulation are again done. In S600, a decision is made about whether an amount of variation in dimension due to the light proximity effect converges or not, and if it does not converge, returning S300, similar steps are conducted. On the other hand, if the amount of variation in dimension due to the light proximity effect converges, correction of photomask data is completed in S700.
Photomask data for which light proximity effect is corrected can thus be obtained by repeating light distribution and development simulations until the amount of dimensional variation due to the light proximity effect converges.
According to the conventional method of correcting the light proximity effect for photomask pattern data described above, the simulation is run based on the photomask pattern data. Because of limitations of the device, an area for which the simulation can be done at a time is at most 1.times.10.sup.-4 mm.sup.2. The regular size of the entire photomask pattern is 4.times.10.sup.2 mm.sup.2, so that four million calculations are necessary in order to do one simulation for one photomask pattern. As described referring to FIG. 14, the time required for calculation in the simulation is considerable since the simulations are repeated until the amount of dimensional variation due to the light proximity effect converges.